Different types of wind turbines having an essentially vertical shaft and an essentially horizontal axis or even an essentially vertical axis are known.
The demand for energy increases constantly as fossil fuel reserves diminish.
This is why electrical companies are beginning to integrate wind turbine energy with other conventional energy sources. Thus, numerous wind turbine power stations have been installed.
Most wind turbines designed for energy production include a rapid asynchronous generator coupled to a multiplier, itself driven by the hub on which the wind turbine blades are mounted. Mention may be made especially of Micon wind turbines.
For example, a 1500-rpm asynchronous generator and a multiplier driven at a speed of 27 rpm correspond to 600 kW.
All these elements are placed in a nacelle, rotationally mounted to one end of the shaft. The height of the shaft is generally between 30 and 60 m.
Also within the nacelle is a nacelle orientation control system and, in some cases, a blade angle of attack control system. This allows the blades to be oriented as a function of the wind. In particular, if the wind becomes too strong, the pitch relative to the wind is modified for reasons of exploitation and safety.
These systems, such as the multiplier, require the presence of at least one hydraulic generator in the nacelle.
A global wind turbine control system is generally provided. It uses a controller that may control the blade angle of attack, the nacelle position, and/or the coupling of the generator to the supply network.
As the asynchronous generator has one or two fixed speeds, its operation on the supply network is not optimal over the entire range of wind speeds.
Low-speed directly driven wind turbines have also been installed. Of note are those manufactured by Enercon. They include a large-diameter radial-flux synchronous machine. The rotor disc of the machine is driven by a shaft, which, in turn, is driven by the wind turbine blades.
The synchronous machine feeds the supply network through an ac-dc-ac converter. Such a converter allows the supply network to be fed at the appropriate frequency and voltage.
In such wind turbines, all the control systems are electrical, especially those that ensure blade pitch or nacelle orientation, as well as the braking system.
These wind turbines allow dispensing with the multiplier and the hydraulic generator. They can also deliver power even at low wind speed.
However, they include an air-cooling system that generates a significant noise level.
In addition, the presence of rotor field windings implies excitation losses that become appreciable at low wind speeds, significantly diminishing the efficiency of the assembly.
Finally, the power of the synchronous machine is necessarily limited by the diameter of the rotor.
Excitation of such a machine with a wound rotor implies either the use of a set of slip rings and brushes, constraint of maintenance generators, or the inclusion of an auxiliary ac exciter and a set of shaft-mounted rectifiers, which further increase the mass of the assembly.
It may be noted also that, in general, wind turbine assembly is difficult. It requires very tall cranes able to lift heavy members of great bulk. Thus, assembly requires a significant engineering effort. For that reason, assembly of such wind turbines in countries that do not have the appropriate equipment at their disposal is not possible.